Multiple Sclerosis (MS) is a disabling inflammatory and neurodegenerative disease for which there is no cure. This proposal details laboratory studies to be carried out in conjunction with a Phase I clinical trial that will assess the MS-relevant in vivo immunologic effects of autologous mesenchymal stem cell (MSC) transplantation. MSCs have been demonstrated, in laboratory experiments, to have potent effects on immune cells relevant to MS pathogenesis, including T- cells, B-cells, NK cells, and antigen-presenting cells. Assessing the activity on these cells pre- and post-MSC infusion will help to determine the range, magnitude, time-course, and inter- patient variability of immunomodulatory effects of MSC transplantation. This study will characterize the activity and immunologic parameters of the immune cell subsets before and after MSC transplantation through flow cytometry and functional assays; assess the relationship of immune changes following MSC transplant to clinical and imaging efficacy measures and adverse effects; and finally assess the mechanisms involved in the immunomodulatory effects resulting from MSC transplant by comparing control and MS MSC effects on peripheral blood cells in vitro. The in vivo immunologic effects in MS and other autoimmune diseases are largely unexplored as most information has been the result of in vitro and animal experiments. These studies may provide insight into immune mechanisms involved in MS. MSC transplantation is also being tested in a large number of other conditions. Thus, our studies may identify immunologic effects of MSCs with broad implications. In the clinical trial, we will evaluate the safety of MSC transplantation and, in a preliminary way, effects on disease activity. The proposed ancillary studies will allow us to further understand the immunological basis of potential adverse effects or clinical benefit. Assessing the immunologic changes in concert with clinical assessments will provide a complimentary series of data which will be helpful in development of MSC transplantation as an MS therapy. If the clinical trial indicates that MSC transplantation is safe and potentially beneficial in MS patients, future clinical trials will be pursued. The proposed ancillary studies will help in the planning of those future trials.